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Battery fuse and CB


gryphon25

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29 minutes ago, gryphon25 said:

On a 2000w inverter with 12v battery do I use a 200a fuse and a 200 amp CB?

My take on this is the inverter will look after itself, it has a suitable  built-in  rated fuse or fuse array to protect its internals. 

The external fuse therefore should be rated to protect your battery and cables more than anything else. This will be dependant on the battery size, but the inverter will not demand more than 170A (plus a bit more for surges) so 200A is fine. But this means your battery should be at least 200Ah 1C. 

By CB you mean an isolator? If so, its just there for isolation, not overload protection (the fuse is enough protection) . You therefore select a breaker that can operated at the 200A minimum, but its ok if its rating is even much higher. 

Edited by BritishRacingGreen
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9 hours ago, gryphon25 said:

So I would use a smaller fuse if I use, say a 120ah battery?

Would the fuse need to change if I use 2 120ah batteries in parallel?

 

Yes, I meant isolator.

Correct, you need to size that fuse so you dont overload the rating of the battery,otherwise you ultimately damage it when there is a sustaimed load demand thats above its specification. 

 

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1 hour ago, BritishRacingGreen said:

Correct, you need to size that fuse so you dont overload the rating of the battery,otherwise you ultimately damage it when there is a sustaimed load demand thats above its specification. 

 

One more thing, if you cold start your inverter with the battery,it is not feasible to just close the fuse or breaker to make contact. The internal capacitors takes a huge hiding with inrush current. If you using lead acids, put a 60w incandescent globe over the fuse to allow a precharge of 20 seconds. Then remove lamp and close fuse or breaker. You will notice no arcing anymore. 

If you have a lithium, it has built in precharge, but only if you close the circuit with the bms on-off switch, ie the breaker and fuse must already be closed. 

Edited by BritishRacingGreen
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